X-Fi output DC offset measuring with original UK X-Fi, no heatsink and L+R channel NJM4556 opamp, rest NJM4558 opamps
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L: 29.9mV DC, 9.8mV AC
R: 29.6mV DC, 9.8mV AC
RL: 0mV DC, 9.8mV AC
RR: 0mV DC, 9.8mV AC
CENTER: 0.2mV DC, 9.6mV AC
SW: 0.2mV DC, 9.7mV AC
X-Fi output DC offset measuring with LM4562 opamps
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L: -190mV DC, 10mV AC
R: -174mV DC, 10.2mV AC
RL: -210.2mV DC, 10.1mV AC
RR: -204.7mV DC, 10mV AC
CENTER: -209.5mV DC, 10mV AC
SW: -231.9mV DC, 10.2mV AC
X-Fi output DC offset measuring with AD8599 opamps
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L: -219mV DC, 9.5mV AC
R: -205mV DC, 9.8mV AC
RL: -209mV DC, 9.7mV AC
RR: -205mV DC, 9.3mV AC
CENTER: -210mV DC, 9.6mV AC
SW: -232mV DC, 9.7mV AC
The 9 - 10mV AC is a classic noise, around 5kHz. What is interesting is the VERY LOW DC offset on RL/RR as well as on CENTER/SUB channels of the original X-Fi (yours), while the L/R show around 30mV of DC offset, so not perfect at all, even at default. Looks like the X-Fi electronic design is perfectly finetuned for a NJM4558 (very low, next to none DC offset), while any other opamp is a problem there.
I think I should short the coupling caps between DAC and opamps first and then measure DC offset again with the original 4558 opamps...
Lokonsky - Quote:
how i measured this dc offset? |
I did using my scope, you have to do the very same.
Quote:
i see people write -200mV and 10 mV what that is mean? |
Value in milivolts (1/100 of V) that represent the value of DC offset on the outputs.
Quote:
Yep, maybe it's safe for my amp but MAYBE not for my headphone...sorry but i very-very new in this |
Well, I tested it for couple of days and it worked fine with my headphones, so... it will with yours too.
Quote:
Other thing, is it good to use solid capacitor in C16,C46 and C72 (470uF/6.3v)? |
Definitively not. I have couple that will fit there nicely and they pack a good deal more ripple current that the Samxon GD 470uF 6.3V d6.3, but polymers are very special caps, optimizes for high (way too high for audio, let's talk about 100kHz and more) operating frequency and they suxx BADLY at low frequency in the audio range.
For example a electrolyte cap Samxon GA has - as most others and polymers too - it's max allowable ripple current stated for 100kHz. At different frequency, there are different multipliers that need to be applied to the rated current to get the max allowable rupple current of that frequency. For 120Hz the multiplier is 0.5 ... However for polymer caps, and they are pretty much all the same, is the multiplier 0.05 (!!!) - Samxon ULR as well as all others (some has even lower multiplier...)...
So you see, using polymers are very specific and are NOT RECOMMENDED AT ALL for any audio applications at all. I always laugh my ***** off at the polymer-only soundcards or mainboard using polymers for audio... but, well...
So as you can clearly see, polymers with the multiplier 0.05 has no chance in 120Hz (and let's not even mention 50Hz). So
polymers are good for output phase of hi-frequency VRM circuits and nowhere else. This nicely demonstrating and confirming the design of Intel D955XCS mainboard - or the overclockers mobo Intel D975XBX "Bad Axe":